The recent adoption of wireless networks in industrial environment has significantly accelerated the development of networked control, in which, the network system and control system work cooperatively to achieve the best performance control. The network system provides real-time data delivery to the control system to make the best control decision. The control system feedbacks its control requirements to the network system to delivery data based on control priority. The network system must delivery data based on criteria that benefit control system the most. However, due to such an increase in wireless networks, the frequencies used for transmission become crowded, and cause significant problems, such as collision and interference of concurrent transmissions.
For example, in an industrial environment, there can be hundreds of production equipment controlled by many different controllers. Wherein, each controller is designed to control certain types of equipment, this combination or pair, forms a control loop. The controller controls the operations of the equipment via a network system and the equipment provides feedback status and measurements back to the controller, through a same or an alternative network system. The controller can directly communicate with multiple equipment, or on the other hand, the equipment can also directly communicate with multiple controllers. However, problems occur when these controllers cooperatively schedule control packet and status packet transmission for whole system to minimize packet latency and to maximize system throughput. For example, throughput becomes a significant issue, among many issues, one such issue includes collision/interference of concurrent transmissions resulting in long delays. These long delays are simply inacceptable in the industrial control system environment.
Another example, is in a cellular environment. A base station communicates with multiple mobile devices, or on the other hand, a mobile device can be within communication of multiple base stations. However, like the above noted industrial environment example, problems in the cellular environment also occur when base stations cooperatively schedule downlink and uplink data transmission to achieve a system level optimization. For example, throughput becomes a significant issue, among many issues, including collision/interference of concurrent transmissions that also result in long delays. These long delays are also simply inacceptable in the cellular environment.
Regarding U.S. Pat. No. 7,830,834 B2, the wireless communication network includes a network coordinator assigning time slots and channels to nodes to provide collision-free scheduling. Each node sends the status information to network coordinator in TDMA mode. However, only one node can transmit packet at a given time slot. Concurrent transmissions can only take place on different frequency channels.
Accordingly, there is a need for devices and methods to provide scheduling technologies for industrial control systems, or other control systems, so as to maximize interference free (collision-free) concurrent transmissions.